NBC reported that the Golden Globe winner and the businessman are splitting up, after two years of dating and sometimes living together.
Garner, who shares three kids with ex-husband Ben Affleck, first sparked romance rumours with Miller in October 2018.
“Yes, she’s been dating John Miller. It’s not serious,” a source told E! News at the time.
“She’s been hanging out with him for the last few months and getting to know him. They have some friends in common and know some of the same people through their kids.”
While Garner and Miller kept their relationship very private over the years — with only a few public outings — E! News learned in early 2020 that they were still together.
“Jen still sees John and seems content with where things are in their relationship,” one insider told E! News in late February.
“John is a nice normal guy who is in a similar situation with raising kids while being divorced. They’ve made what they have work and enjoy being together.”
Garner, 48, was first married to actor Scott Foley(2000-2004) and then married Afleck for 13 years(2005-2018).